CODEWITHSUNDEEP
objective-ciosautomatic-ref-counting
Nosrettap
Nosrettap

Reputation: 11320

A few questions about ARC for iOS?

I'm fairly new to ARC for iOS (and pretty new to iOS in general) and I have a few quick questions about ARC.

~ In a View Controller, if I do not have statements in my viewDidUnload() method setting my properties to nil, will the properties' memory still be freed when my view controller is released? If so, why do I need to explicitly have this viewDidUnload method?

~ In objects that are not View Controllers, where should I set the properties to nil at? In dealloc? What about primitive properties such as @property BOOL isActive;...do I need to set them equal to nil/zero?

Thanks.

Upvotes: 1

Views: 321

Answers (3)

Steven Fisher
Steven Fisher

Reputation: 44856

  1. You don't need to set your properties to nil as long as they're weak references. IBOutlets should generally be weak references, since they the view controller contains a strong reference to the view, which in turn contains strong references to all of its subviews. (If you have IBOutlets that aren't part of that view hierarchy, they should be strong.)
  2. You shouldn't need nil or zero anything, objects or scalars. Xcode will insert nilling statements when working with Interface Builder, but this is it still generating code for pre-ARC Objective-C.

You probably don't even need a viewDidUnload; it's only called in special circumstances, when there's low memory stress. Thus, you can't depend on it for cleaning up. Your IBOutlets should be weak, so they'll be cleaned automatically when the view is purged from the viewcontroller (and they'll be restored if the view is reloaded).

I'm assuming here that you're writing a new product, which means you're targeting iOS 5 or later only. If you're targeting iOS 4 in a new product, you really shouldn't be. The world has moved on, with 80% of the market on iOS 5 or later. And that's today. Going forward, it's going to be even harder to avoid iOS 5 features for an even smaller percentage of people.

Upvotes: 4

Michael Mangold
Michael Mangold

Reputation: 1801

Memory management for @properties is handled automatically under ARC. For times when you have set yourself as delegate, it is common to set the delegate to nil before going away (in viewWillDisapear for instance) so that future calls to delegate don't reference garbage. Stay tuned for the soon-to-be-posted WWDC videos for the latest guidance.

Upvotes: 1

Kendall Helmstetter Gelner
Kendall Helmstetter Gelner

Reputation: 75058

In viewDidUnload you need to set outlet references to nil, because ARC will release them and you do not want to accidentally use them after that happens.

You don't have to do anything with properties, they will be handled automatically. In fact you really do not normally even have a dealloc method any more with ARC.

Upvotes: 0

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